VARIABILITY OF THE NEAR-SURFACE EDDY KINETIC-ENERGY IN THE CALIFORNIACURRENT BASED ON ALTIMETRIC, DRIFTER, AND MOORED CURRENT DATA

Low-pass-filtered velocities obtained from World Ocean Circulation Exp eriment (WOCE) surface drifters deployed in the California Current off northern California during 1993-1995 have been compared with surface geostrophic velocity estimates made along subtracks of the TOPEX/POSEI DON altimeter and with moored acoustic Doppler current profiler (ADCP) data. To obtain absolute geostrophic velocities, a mean sea surface h eight (SH) field was estimated using the mean drifter velocities and h istorical hydrographic data and was added to the altimetric SSH anomal ies, The correlation between collocated drifter and,altimetric velocit ies is 0.73, significant at the 95% level. The component of the drifte r velocity which was uncorrelated with the altimetric velocity was cor related with the wind in the Ekman transport sense. Monthly averages o f eddy kinetic energy (EKE), estimated using all drifter and altimeter data within the domain (124 degrees-132 degrees W, 33 degrees-40.5 de grees N), show energy levels for the drifters that are about 13% great er than those for the altimeter. Drifter, altimeter, and ADCP measurem ents all exhibit similar seasonal cycles in EKE, with the altimeter da ta reaching maximum values of about 0.03 m(2) s(-2) in late summer/fal l. Wavenumber spectra of the altimeter velocity indicate that the velo city fluctuations were dominated by features with wavelengths of 240-3 70 km, while the ADCP data suggest that the temporal scales of these f luctuations are at least several months. Between 36 degrees and 40.5 d egrees N, the region of monthly maximum EKE migrates westward to about 128 degrees W on a seasonal timescale. This region of maximum EKE coi ncides with the maximum zonal SSH gradient, with increased EKE associa ted with. increased southward flow. A simple model shows that much of the seasonal cycle of the SSH anomalies can be produced by linear prod esses forced by the curl of the wind stress, although the model cannot explain the offshore movement of the front.